1. Field of the Invention
The present invention relates to a glass-ceramics composite material. More particularly, the present invention relates to a glass-ceramics composite material which is suitable for the low-temperature firing use and has high moisture resistance and thermal conductivity.
2. Description of Related Art
For example, in the circuit substrate applied to a semiconductor package, a multi-layer circuit substrate, etc., suppression of the loss by reduction of the electrical resistance of the conductor which constitutes wiring and improvement of the heat resistance responding to increase of the heat generated from a semiconductor device has been an important subject. As a measure over the former, for example, metal which has low electrical resistance (good conductor), such as gold, silver, copper, and an alloy containing such metal is widely used. On the other hand, as a measure over the latter, a ceramic substrate using ceramics as a base material is widely used in place of a resin substrate using resin as a base material.
In such a ceramic substrate, as mentioned above, the conductor which constitutes a surface electrode and inner layer wiring comprises a good conductor, such as gold, silver, copper, and an alloy containing such metal, for example. Thereby, in such a ceramic substrate, for example, even when highly fine inner layer wiring is disposed for the purpose of improving the performance of a semiconductor package, etc., increase of the electrical resistance of wiring can be suppressed and the resistance loss in the semiconductor package which uses the ceramic substrate can be reduced.
By the way, the metal (low resistance metal) which has low electrical resistance, such as gold, silver, copper, and an alloy containing such metal, which is used for the purpose of suppressing increase of the electrical resistance of wiring as mentioned above, has a relatively low melting point as compared with other metal. When a sheet of dielectric material (base material consisting of dielectric layer(s)) in which a conductive pattern (wiring) comprising such a low resistance metal is embedded is simultaneously fired at a temperature higher than the melting point of the metal, there is a possibility that the metal may melt and it may become difficult to maintain the desired shape of the conductive pattern. Therefore, when such a low resistance conductor is used as a conductor which constitutes a surface electrode and inner layer wiring, it is desirable to use ceramics which can be fired at a temperature lower than the melting point of the low resistance conductor used.
In addition, it is desirable to use what is called low temperature fired substrate material (LTCC: Low Temperature Co-fired Ceramics) as the ceramic that can be fired at a temperature lower than the melting point of the low resistance conductor.
For example, a glass-ceramics composite material which has its firing temperature lowered by blending a glass component into ceramics is generally used as an LTCC. Even when gold, silver, copper, or an alloy containing such metal, is used as a low resistance conductor having a relatively low melting point the possibility that the metal may melt making it difficult to maintain the desired shape of the conductive pattern when being fired simultaneously together with the base material can be reduced by using such LTCC materials.
For example, in semiconductor elements, such as a power semiconductor element, as a loss remedy, silicon carbide (SiC) wafers and/or gallium nitride (GaN) wafers are being used widely in place of silicon (Si) wafers used conventionally. The power semiconductor elements which use these new types of wafer (for example, SiC-MOSFET, GaN-HEMT, etc.) have a feature that operation at a higher temperature is possible, as compared with the power semiconductor element which uses the conventional Si wafer. Thereby, the cooling mechanism indispensable in the power semiconductor element which uses the conventional Si wafer (for example, a heat sink, a water-cooled mechanism, etc.) can be simplified drastically. As a result, reduction in size and weight of the power module including the power semiconductor element can also be attained by using these new types of wafer.
However, the temperature in the surroundings of the power semiconductor element is higher than before due to the rise of the operating temperature and reduction in size and weight of a power module as well as the simplification of a cooling mechanism accompanying use of the new types of wafer as mentioned above. Therefore, there is an increasing demanded for a ceramic substrate used for a power semiconductor element to demonstrate not only even higher heat resistance, but also higher thermal conductivity than before.
In the art, in response to such a demand, for example, it has been proposed to add particles having high thermal conductivity, such as aluminum nitride (AlN) particles and silicon carbide (SiC) particles, etc. (high thermal conductive particles) as filler particles to the glass-ceramics composite material which constitutes the base material of the ceramic substrate which has the inner layer wiring consisting of low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, for example (for example, refer to Patent Literatures 1 to 8).
Moreover, it has been proposed to blend spinel system compound crystal phases and such as gahnite (ZnAl2O4) and/or spinel (MgAl2O4), as well as at least one kind of non-oxide system compound crystal phase chosen from the group of aluminum nitride (AlN), silicon nitride (Si3N4), silicon carbide (SiC), and boron nitride (BN), into a glass phase comprising as a main component silicon oxide (SiO2), aluminum oxide (Al2O3), zinc oxide (ZnO), magnesium oxide (MgO), and boron oxide (B2O3), for the purpose of raising the intensity and the thermal conductivity of a base material effectively (for example, refer to Patent Literature 9).
As mentioned above, in the art, various technology which raises the thermal conductivity of a glass-ceramics composite material by adding, for example, non-oxide system compound crystal phase, such as aluminum nitride (AlN) etc., as filler particles, to a glass-ceramics composite material has been proposed.
In the glass-ceramics composite material used as LTCC, for example, from a viewpoint of securing the properties required for LTCC, such as improvement in the workability at the time of dissolution of a glass phase, reduction of firing temperature, and improvement in the strength and thermal conductivity by increasing the degree of densification, etc., it is thought that it is important to lower the melting point and/or the softening point of a glass phase. In order to lower the melting point of a glass phase, it is effective to add a flux component, for example, such as boron oxide (B2O3), to a glass phase. However, a glass phase containing large quantity of boron oxide (B2O3) has poor moisture resistance, and concern remains about the reliability under high temperature and high humidity circumstance, for example, when it is used as a material of the substrate (electronic circuit card) on which an electronic circuit element is mounted, for example.
As mentioned above, in the art, demand for a glass-ceramics composite material suitable for a low-temperature firing use, which has high moisture resistance and thermal conductivity, has been existing.